Self-Assembled Molecular Platforms for Bacteria/Material Biointerface Studies: Importance to Control Functional Group Accessibility

Highly controlled mixed molecular layers are crucial to study the role of material surface chemistry in biointerfaces, such as bacteria and subsequent biofilms interacting with biomaterials. Silanes with non-nucleophilic functional groups are promising to form self-assembled monolayers (SAMs) due to their low sensitivity to side-reactions. Nevertheless, the real control of surface chemistry, layer structure, and organization has not been determined. Here, we report a comprehensive synthesis and analysis of undecyltrichlorosilane- and 11-bromoundecyltrichlorosilane-based mixed SAMs on silicon substrates. The impact of the experimental conditions on the control of surface chemistry, layer structure, and organization was investigated by combining survey and high-resolution X-ray photoelectron spectroscopy analysis, wettability measurements, and ellipsometry. The most appropriate conditions were first determined for elaborating highly reproducible, but easily made, pure 11-bromoundecyltrichlorosilane SAMs. We have demonstrated that the control is maintained on more complex surfaces, i.e., surfaces revealing various chemical densities, which were obtained with different ratios of undecyltrichlorosilane and 11-bromoundecyltrichlorosilane. The control is also maintained after bromine to amine group conversion via S_N2 bromine-to-azide reactions. The appropriateness of such highly controlled amino- and methyl-group revealing platforms (NH₂–<i>X</i>%/CH₃) for biointerface studies was shown by the higher reproducibility of bacterial adhesion on NH₂–100%/CH₃ SAMs compared to bacterial adhesion on molecular layers of overall similar surface chemistry but less control at the molecular scale

Hydrothermal Synthesis and Characterization of Bio-Sourced Macroporous Zinc Phosphates Prepared with Casein Protein

The development of an original and simple procedure of hydrothermal porous biosourced zinc phosphates synthesis from casein protein is reported in this study. The synthesis procedure does not require additional phosphorus source and structure-directing agent for macroporosity formation. The formation of zinc phosphates has been investigated as a function of the pH of the starting mixture (4.5–14.0) and of the temperature of calcination (from 150 to 750 °C). A material composed of hopeite (Zn₃(PO₄)₂·4H₂O) and casein was obtained after synthesis at pH 4.5 and 100 °C from a mixture of casein and zinc nitrate solutions. Macroporous zinc phosphates composed of α-Zn₃(PO₄)₂ and α-Zn₂P₂O₇ with large porous size distribution (pore diameter between 350 to 1000 nm) were successfully obtained after the complete casein decomposition at 750 °C. Samples were characterized by X-ray powder diffraction, solid-state ³¹P NMR spectroscopy, thermal analysis, scanning electron microscopy, nitrogen adsorption, and by fluorescence spectroscopy. The macroporous zinc phosphates have a good stability in water for at least 24 h with no detectable change in their structure, porosity, and crystal morphology

Tuning InAs Nanowire Density for HEK293 Cell Viability, Adhesion, and Morphology: Perspectives for Nanowire-Based Biosensors

Arrays of nanowires (NWs) are currently being established as vehicles for molecule delivery and electrical- and fluorescence-based platforms in the development of biosensors. It is conceivable that NW-based biosensors can be optimized through increased understanding of how the nanotopography influences the interfaced biological material. Using state-of-the-art homogenous NW arrays allow for a systematic investigation of how the broad range of NW densities used by the community influences cells. Here it is demonstrated that indium arsenide NW arrays provide a cell-promoting surface, which affects both cell division and focal adhesion up-regulation. Furthermore, a systematic variation in NW spacing affects both the detailed cell morphology and adhesion properties, where the latter can be predicted based on changes in free-energy states using the proposed theoretical model. As the NW density influences cellular parameters, such as cell size and adhesion tightness, it will be important to take NW density into consideration in the continued development of NW-based platforms for cellular applications, such as molecule delivery and electrical measurements

Tuning InAs Nanowire Density for HEK293 Cell Viability, Adhesion, and Morphology: Perspectives for Nanowire-Based Biosensors

Arrays of nanowires (NWs) are currently being established as vehicles for molecule delivery and electrical- and fluorescence-based platforms in the development of biosensors. It is conceivable that NW-based biosensors can be optimized through increased understanding of how the nanotopography influences the interfaced biological material. Using state-of-the-art homogenous NW arrays allow for a systematic investigation of how the broad range of NW densities used by the community influences cells. Here it is demonstrated that indium arsenide NW arrays provide a cell-promoting surface, which affects both cell division and focal adhesion up-regulation. Furthermore, a systematic variation in NW spacing affects both the detailed cell morphology and adhesion properties, where the latter can be predicted based on changes in free-energy states using the proposed theoretical model. As the NW density influences cellular parameters, such as cell size and adhesion tightness, it will be important to take NW density into consideration in the continued development of NW-based platforms for cellular applications, such as molecule delivery and electrical measurements

Biomimetic Cryptic Site Surfaces for Reversible Chemo- and Cyto-Mechanoresponsive Substrates

Chemo-mechanotransduction, the way by which mechanical forces are transformed into chemical signals, plays a fundamental role in many biological processes. The first step of mechanotransduction often relies on exposure, under stretching, of cryptic sites buried in adhesion proteins. Likewise, here we report the first example of synthetic surfaces allowing for specific and fully reversible adhesion of proteins or cells promoted by mechanical action. Silicone sheets are first plasma treated and then functionalized by grafting sequentially under stretching poly(ethylene glycol) (PEG) chains and biotin or arginine-glycine-aspartic acid (RGD) peptides. At unstretched position, these ligands are not accessible for their receptors. Under a mechanical deformation, the surface becomes specifically interactive to streptavidin, biotin antibodies, or adherent for cells, the interactions both for proteins and cells being fully reversible by stretching/unstretching, revealing a reversible exposure process of the ligands. By varying the degree of stretching, the amount of interacting proteins can be varied continuously